Fixture for stretching sheet metal



July 23, 1968 c. J. BATH FIXTURE FOR STRETCHING SHEET METAL 4 Sheets-Sheet 1 Filed May 16, 1966 ZQTOR. 9 45 ATTORNEY July 23, 1968 c. J. BATH 3,393,548

FIXTURE FOR STRETCHING SHEET METAL Filed May 16, 1966 4 Sheets-Sheet 2 C 611w]; TOR. BY 5 a, I IL I Q ATTORNEY July 23, 1968 c. J. BATH 3,393,548

FIXTURE FOR STRETCHING SHEET METAL 4 Sheets-Sheet 5 Filed May 16, 1966 INVENTOR.

P27 .4. I QM ATTORNEY.

July 23, 1968 c. J. BATH 3,393,548

FIXTURE FOR STRETCHING SHEET METAL Filed May 16, 1966 4 Sheets-Sheet 4 INVENTOR. 8 412-45424, BY 2 I 5 1;

- ATTORNEY.

United States Patent 3,393,548 FIXTURE FOR STRETCHING SHEET METAL Cyril John Bath, Chagrin Falls, Ohio, assiguor to The Cyril Bath Company, Cleveland, Ohio, a corporation of Ohio Filed May 16, 1966, Ser. No. 550,520 Claims. (Cl. 72-496) This invention relates to a stretching fixture for stretching sheet metal undimensionally into a range above its elastic limit preparatory to the formation of the metal about a male die or by the cooperation of companion male and female drawing dies. This is an improvement in the inventions disclosed in US. Letters Patent of Paul F. Maize, No. 3,113,607, issued Dec. 10, 1963, and of Cyril J. Bath, No.,3,1l6,7 80, issued Jan. 7, 1964,.and in the co-pending application of Robert A. Mackenzie, Ser. No. 514,219, filed Dec. 16, 1965, and entitled Prestretch Fixture and Combination Thereof with Drawing Die Press, now abandoned in favor of a copending continuation-in-part application, Ser. No. 575,489, filed Aug. 12, 1966, now PatentNo. 3,314,269, issued Apr. 18, 1967.

For the purposes of illustration, the invention is described hereinafter as applied to combined stretching and draw die drawing of sheet metal in a stretch draw press, its use for stretching the metal across the male die without the application of a female die being readily apparent from the illustrative example.

As disclosed in the above patents and application, in the stretch drawing of sheet metal unidimensionally, usually two stretch units are arranged on the bed of an upright drawing press on opposite sides of the die space. The units are provided with heads arranged to grip and tension the sheet metal stock unidimensionally while applying it to a male die or while it is drawn between companion drawing dies. Though generally two units are employed, one at each side of the die space, a single stretch unit may be employed at one side of the die space and a fixed gripping head arranged at the opposite side.

Each unit comprises generally a gripping head ha'ving jaws which clamp onto the adjacent margin of the sheet stock. The head may be moved away from the die space either by suitable power means and toward the die space by the power means or by the sheet itself.

In the above patents, the heads are yieldably urged away from the die space by hydraulic piston and cylinder assemblages and are drawn toward the die space by the metal itself as the metal is wrapped about the male die.

In the above application, the heads are moved positively by rigid links both toward and away from the die space. In both instances, the heads are movable in upright paths concurrently with their movements toward and away from the die space. To permit these movements of the heads, each head is mounted on a carriage which, in turn, is mounted on an elevator for movement relative thereto in a generally horizontal path toward and away from the die space. The elevator is mounted in suitable upright frames or supports for movement in a vertical path.

As more fully explained in the above identified application, it is desirable that at least at the end of the forming operation as the head approaches the adjacent margin of the male die the head be in a position in which its loading face faces toward, and can approach the die so closely that substantially only the margin of the metal actually being gripped by the jaws of the head is wasted in trim. This position of the head is best attained by constraining the head to move at all times parallel to its starting position.

In Patent No. 3,113,607, this parallel relation is obtained by mounting the head on a carriage which is movable in horizontal slideways on an elevator. In Patent No. 3,116,780, each head is mounted on a carriage which is mounted on an elevator, the inner end of the carriage being guided on the elevator by suitable rollers and its other end being connected by a link to the elevator. The link assists in guiding the head and serves as a means for connecting hydraulic piston and cylinder assemblages to the head for applying stretching force thereto.

In the above-entitled application, the carriage for the head was mounted in the same manner as in the Patent No. 3,116,780, but instead of applying pressure to the head by piston and cylinder assemblages, the tensioning force is applied by suitable links.

With these arrangements, the heads maintained a position parallel, or substantially parallel, to their starting positions at all times during the stretch forming or stretch drawing operation. This position is one in which the loading face of the head faces directly toward the die space or die path.

In accordance with the present invention, the carriages to which the heads are fixedly secured, are connected to the elevators by links. These links are arranged in pairs which are parallel to each other and aligned in a row extending forwardly and rearwardly of the press. All of the links are of equal length and the four pivots of each pair of links define a parallelogram. The parallelograms of all of the pairs of links for each head are identical. Each pivot of each pair of links is coaxial with the corresponding pivots of the other pairs. Thus, the supporting links themselves maintain the heads in positions parallel to their starting position and assure their movement relative to the elevator in a substantially horizontal path.

Specific advantages of the invention reside in the arrangement of the parallelogram linkage supports of the stretch heads which greatly simplifies the structure heretofore employed for a like purpose and reduces the frictional stresses resisting movement of the heads.

Other objects and advantages of the invention will become apparent from the following description wherein reference is made to the drawings, wherein:

FIG. 1 is a front elevation of a drawing die press incorporating the stretching units of the present invention;

FIG. 2 is an enlarged top plan view of one of the stretch units of the invention;

FIG. 3 is an enlarged front elevation of one of the units illustrated in FIG. 1;

FIG. 4 is a further enlarged vertical sectional view of the unit illustrated in FIG. 2, and is taken on line 4-4 thereof; and

FIG. 5 is a front elevation of a set of stretching units and associated dies;

FIG. 6 is a hydraulic diagram of the system used for the press and unit.

Referring to the drawings, the invention is shown incorporated in a conventional upright hydraulic press 1 having a bed 2 with upright guide members 3 arranged at the corners and guiding a ram 4 for vertical reciprocation. The bed supports a male drawing die 5 which has a forming face which is convex upwardly, both transversely and lengthwise. The ram supports a complementary female drawing die 6. The dies 5 and 6 define, when closed, a c'oncaivo-convex pattern or patterns into which the sheet metal is drawn by the dies. The stock is tensioned by the stretch units along one dimension only, and conventional hold down rings or devices are not employed.

The ram is driven on its forming and return strokes by means of hydraulic piston and cylinder assemblages 7, including cylinders 8 and pistons 9 having piston rods 10 secured to the ram.

Stretch units 11 are mounted on the bed 2 adjacent those margins of the die which are opposite from each other in the tensioning dimension. These margins, for

brevity in description, are referred to hereinafter as the end margins even though the tensioni'ng dimension is the shorter dimension of the sheet.

As more fully described in the above application, each unit 11 comprises a base plate 13 on the front and rear of which are mounted guide supports 14 which support upright guides 15. Each guide 15 has upright slide surfaces 16 facing inwardly of the unit in a direction forwardly and rearwardly of the bed, and upright guide faces 17 at right angles to the surfaces 16. Mounted for vertical reciprocation in the slideways is a stretch head elevator 20 which is guided thereby for movement upwardly and downwardly while the elevator itself remains parallel to its starting position.

For moving the elevator 20 upwardly and downwardly, suitable piston and cylinder assemblages 21 are provided, one at each end of the elevator. Each assemblage comprises a cylinder 22 mounted in fixed position on the elevator. A piston 23, having a piston rod 24, is reciprocable in the cylinder. The cylinder 22 is arranged so that the piston rod extends downwardly and its lower end carries a tongue 25 by which it is pivotally connected by a horizontal pivot 26 to a suitable yoke 27 which is fixedly secured to the base 13 of the associated unit. Thus, upon introduction of the hydraulic pressure fluid to the rod ends of the cylinder 22, they move the elevator downwardly, and by introduction of the fluid to the head end of the cylinders, they move the elevator 20 upwardly. These movements are under yieldable hydraulic pressure and are controllable independently of the operation and control of the ram piston and cylinder assemblages 7. The elevators are also controllable independently of each other.. Thus the elevators can be raised and lowered independently of each other and of the ram in preselected variable relation with respect to the rise and fall of the ram.

In order to tension and stretch the stock independently of the stretching caused by die closure, suitable stretch heads 30 are provided, one for each unit 11. Each head comprises an elongated body 31 which, lengthwise, extends forwardly and rearwardly of the press bed and thus transversely of the dimension in which the stock is to be tensioned. Each head has complementary gripping jaws 32 and 32a which are opened and closed by links 33 and 34.

As hereinbefore mentioned, it is desirable that each stretch head move at all times parallel to its loading or starting position wherein its inner or loading face, which is the face through which the jaws open for receiving the margin of the sheet of metal to be stretched and formed, is generally upright and facing toward the ends of the dies. This permits the portion of the sheet between the heads to be subjected to the dies substantially to the inner faces of the heads, thus utilizing all the metal which is not actually being gripped by the jaws themselves.

In order to constrain each head to movement parallel to its original position, each head is connected in fixed position on an associated carriage 40. Connecting blocks 41 are provided on the under side of the carriage near the inboard margin of the carriage which is adjacent the die space. A set of inboard links 42 are pivotally connected at their upper ends to blocks 41 by coaxial pivots 43. The links 42 are pivotally connected at their lower ends by coaxial pivots 44 to blocks 45 which are connected to the bottom wall of the elevator 20.

Connecting blocks 46 are provided on the underside of the carriage 40 near the outboard margin which is disposed outwardly from the die space. A set of outboard links 47 are pivotally connected at their upper ends by coaxial pivots 48 to the blocks 46. At their lower ends the links 47 are connected by pivots 49 to fixed blocks 50 on the bottom of the elevator. The pivots 43, 44, 48 and, 49, are parallel to each other and all links are of equal length. The. pivotal axes are so positioned that, when viewed axially, they define a parallelogram.

The links preferably are arranged in pairs, each pair j 4. I v comprising an inboard link and an outboard link whose connections provide a parallelogram. The number of pairs of links 42 and 47 depends upon the length of the stretch head in a direction forwardly and rearwardly of the stretch head. The pairs may be distributed along the length of the head, as required, generally about eight pairs of links being satisfactory for a sixty inch head.

As a result of this connection between the links 42 and 47 and the elevator 20 and head 30, the head 30 may be moved toward and away from the die space relative to the elevator 20 in paths which are generally horizontal relative to the elevator. Concurrently the elevator may be moved along its upright path. As a result, all movements desired by the heads are provided. a

The advantage of connecting the lower ends of the links 42 and 47 at the bottom of the elevator is to obtain as great a length of the links as practicable so that the path of the 'head 30 relative to the elevator 20 is substantially chordal and horizontal. The head is maintained at all times parallel to its starting position.

If hydraulic cylinders are to be used to apply the tensioning force to the heads, such can be connected to the links 42 or the links 47 in much the same manner as they are connected to the links in the above identified Patent No. 3,116,780, or they may be connected to cross-bars which, in turn, are connected to both groups.

In order to move the heads toward and away from the dies as they are raised and lowered, the heads are connected to suitable links which swing about pivots which are fixed in relation to the male die on the bed. As illustrated in FIG. 5, one of the heads 30 is connected to one end of a set of links 6% by means of coaxial pivots 61 so that the head can rock relative to its associated links. The links are rigid and of fixed length, and generally two links are provided for each head, one at the front of the head and one at the rear. They function as a single rigid link.

The other ends of these links are mounted on coaxial pivots 62 for swinging about a common axis thereof. The pivots 62 are mounted in fixed position relative to the die 5, and their common axis extends horizontally, transversely of the tensioning dimension, and is below the level of the upwardly facing convex forming face of the die 5.

In the form illustrated, the pivots 62 are mounted directly on the die 5 so that the die, the associated carriage, the associated links, and associated heads can be removed as a unit from the press for storage and reinstalled as a unit.

correspondingly, the other head 30 is connected, by way of its carriage 50, to one end of a pair of links 63 by coaxial pivots 64 so that the head can rock relative to its links 63. The other ends of the links 63 are connected to coaxial pivots 65 which are parallel to the pivots 62 and are in fixed position relative to the die 5, preferably directly on the die so that these links, pivots, head and carriage can also be removed as a unit with the die.

The positions of the pivots and their associated links are such that upon initial downward movement of the heads the links cause the heads to move relatively apart from .each other with non-yielding force to tension the stock to the desired range. When the heads continue downwardly, they may continue to be moved farther apart by the links, at least during a part of their stroke. Usually as they are moved toward the lower portion of their downward path, they cease moving apart and are moved back inwardly toward the die 5 by the links so that their inner or loading faces become positioned finally substantially at the lower edges, respectively, of the ends of the forming face of the die 5. Each head remains always during this travel a fixed distance from the axis of the associated pivot on the die 5. Accordingly, the inward movement of each head requires swinging of the axes of the pivotal connections of the links with the heads inwardly toward the dies.

Having reached this elastic limit and been pulled downwardly around the male die, the heads are controlled so that their inner faces are closely adjacent or substantially at, their associated ends of the dies, respectively, upon final closure of the dies.

The piston and cylinder assemblages 36 for closing the jaws of the head can be operated pneumatically or by hydraulic pressure. In the form illustrated, hydraulic pressure is employed throughout, as illustrated in FIG. 6.

As there illustrated, the press is supplied with hydraulic fiuid by a pump 70 driven by a motor 71. The pump supplies the fluid through a line 72 through a pressure control regulator 73 and a solenoid operated stop and reversing valve 74. Pressure fluid for the jaw closing assemblages 36 and for the elevator piston and cylinder assemblage 21 is supplied by a pump 76 driven by a motor 77, this pump being connected to the assemblage 21 through a stop and reversing valve 78, and being connected to the jaw operating assemblages 36 through a stop and reversing valve 79. Various conventional pressure regulators and relief valves may be employed in the circuit, if desired, but form no part of the invention.

It is apparent that with this arrangement, the proper position of the heads can be maintained positively and effectively at all times. The arrangement is particularly suitable for use in mechanical presses combined with linkages for moving the heads toward and away from the die, push rods for operating the elevators, as disclosed in the above entitled application, and pneumatic pressure for operating the jaws as such make the entire operation, except for pneumatic closure of the gripping jaws, a mechanical operation.

Having thus described my invention, I claim:

1. A tensioning unit for a stretch-draw press and comprising:

a supporting frame;

an elevator mounted thereon for movement generally upwardly and downwardly along a fixed path;

means for moving the elevator along said path;

a stretch head adapted to grip the margin of a sheet of metal stock and operable for tensioning the stock as the head is moved in a path relative to the elevator transversely of the elevator path;

generally upright quadrilateral linkage means pivotally connected at the upper end to the head and at the lower end to the elevator with the pivotal axes extending parallel to each other and transversely of said paths of the head and of the elevator; and

means for moving the head along its path for tensioning the stock.

2. The structure according to claim 1 wherein the linkage means comprises a plurality of inboard links and a plurality of outboard links spaced from the inboard links in a'direction endwise of said path of the head and transversely of the head of the elevator, the inboard and outboard links are arranged in rows, respectively, which extend transversely of said paths of the head and of the elevator, all of said links are of equal length and are parallel to each other.

3. The structure according to claim 1 wherein all of the upper pivotal axes of the linkage means are disposed in a substantially horizontal plane, and all of the lower pivotal axes are disposed in a plane parallel to and spaced below said horizontal plane.

4. The structure according to claim 1 wherein the quadrilateral linkage means comprise a plurality of inboard links and a plurality of outboard links, the inboard links are spaced apart firom the outboard links in the direction endwise of the head path, all of said links are of equal length, upper coaxial pivots connect the upper ends of the inboard links to the head, lower coaxial pivots connect the lower ends of the inboard links to the elevator, additional upper coaxial pivots connect the upper ends of the outboard links to the head, and additional lower coaxial pivots connect the lower ends of the outboard links to the elevator.

5. The structure according to claim 4 wherein said links are arranged in pairs, each pair comprises one inboard link and one outboard link, and the links of each pair are aligned with each other in a direction endwise of said path of the head.

6. The structure according to claim 4 wherein said links are arranged in pairs, each pair comprises one inboard link and one outboard link, and said pairs being aligned with each other in a direction parallel to their pivotal axes.

7. The structure according to claim 1 wherein the quadrilateral linkage means are disposed with their lower pivotal axes near the bottom of the elevator and with their upper pivotal axes near the upper end of the elevator.

8. The structure according to claim 1 wherein the linkage means are parallelogram linkage means and are disposed with the longer side of the parallelogram generally upright.

9. The structure according to claim 1 wherein the quadrilateral linkage means define a rectangular paralleogram when the head is in an intermediate position between the ends of its path.

10. A tensioning unit for a stretch draw press comprising,

a stretch head adapted to grip a margin of a sheet of metal stock and operable for tensioning the stock upon predetermined movement of the head from :a starting position;

supporting means;

a quadrilateral linkage mean-s pivotally connected at one end to the head so that the pivotal axes of the links are parallel to each other and are spaced apart transversely relative to each other, each link being pivotally connected at its opposite end to the sup porting means so that the axes of the pivotal connections of the links with the supporting means are parallel to each other and are spaced apart transversely relative to each other; said quadrilateral linkage means constraining the head to movement in a predetermined fixed path and to movement relative to the supporting means in a predetermined fixed path in which, at the end of the forming operation, the loading face of the head faces toward, and can approach the die so closely that the gripped margin of the metal is substantially at the ends of the dies; and

power means to apply stretching force to the head and for causing said movement of the head from said starting position.

References Cited UNITED STATES PATENTS 2,442,268 5/ 1948 Fields et al 72-297 3,113,607 12/1963 Maize 72-296 3,316,780 1/1964 Bath 72297 3,314,270 4/1967 Dolney 72-296 CHARLES W. LANHAM, Primary Examiner.

R. D. GREFE, Assistant Examiner. 

1. A TENSIONING UNIT FOR A STRETCH-DRAW PRESS AND COMPRISING: A SUPPORTING FRAME; AN ELEVATOR MOUNTED THEREON FOR MOVEMENT GENERALLY UPWARDLY AND DOWNWARDLY ALONG A FIXED PATH; MEANS FOR MOVING THE ELEVATOR ALONG SAID PATH; A STRETCH HEAD ADAPTED TO GRIP THE MARGIN OF A SHEET OF METAL STOCK AND OPERABLE FOR TENSIONING THE STOCK AS THE HEAD IS MOVED IN A PATH RELATIVE TO THE ELEVATOR TRANSVERSELY OF THE ELEVATOR PATH; 